1. Field of the Invention
This application relates broadly to improvements in automatic backwash filtering systems. More particularly, it concerns apparatus and methods for monitoring the turbidity of effluent for control of backwash operations in such systems.
2. Description of the Prior Art
Automatic backwash filter systems are known in the art as exemplified in U.S. Pat. Nos. 3,239,061; 4,133,766; 4,617,131 and 4,764,288 currently assigned to Infilco Degremont Inc., the assignee of the invention disclosed herein. Such systems are further exemplified in Infilco Degremont's brochure DB-370, dated May, 1989, entitled ABW.RTM. Automatic Backwash Filter. The disclosures of these patents and the brochure are incorporated herein by reference.
A principal use of automatic backwash filter systems is to produce potable water in water treatment plants many of which are subject to state or other governmental regulatory agencies that set standards and conditions concerning the operation of the systems and the quality of the effluent. For example, many such agencies require that, following backwash in filter beds of a potable water treatment plant, the effluent from such filter beds can not be placed back on the service line, but must be sent to waste, until their turbidity reaches a predetermined acceptable low level, e.g., &lt;0.25 NTU. When this turbidity level is reached, the filter beds can be put back in service.
The art of measuring turbidity in fluids is well developed and devices for such purpose take many forms ranging from simple viewing tubes to continuous, on-line electronic-type monitors. Hence, the regulatory turbidity restrainst noted above do not present a problem as far as technical measurement of the turbidity in an effluent aliquoit is concerned. However, in order to have efficient operation of an automatic backwash filter system meeting the regulatory turbidity requirements without great increase in equipment costs to attain same, problems are presented in applying known turbidity monitor devices to aliquoits and in utilizing resulting data to assist in the operation of the backwash filter system. The present invention addresses these problems and provides unique apparatus and methods for solving same.